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Séminaire de Yudawati Cahyarini (LIPI Bandung, Java, Indonésie)

Tropical Maritime Climate Variability: Records from Indonesian Corals;

Indonesia is located in the prominent site to study climate variability i.e. which is located between Pacific and Indian ocean. Its geographic location has consequences to the regional climate variability in Indonesia. The Northwest (NW) monsoon cause rainfall in the region of Indonesia, while reversely Southeast (SE) monsoon cause dry season around Indonesia. Indonesia links the Pacific and Indian Ocean and is influenced both by Indian Ocean and Pacific climate events such as the Indian Ocean Dipole (IOD) and the El Nino Southern Oscillation (ENSO). Both climate events have severe global socio-economic consequences, as they may cause serious droughts or floods over adjacent land areas. To better understand these climate phenomenons, it requires long time series of important climatic variables that extent further back in time than the instrumental record. Therefore, paleoclimatic studies which provide climate data back into hundreds to thousands year even to million year are extremely important. Coral Sr/Ca can provide information on past sea surface temperature (SST) and paired Sr/Ca and 18O is used to reconstruct variations in the 18O seawater which further to reconstruct precipitation balance (salinity) at monthly to annual interannual resolution. Several climate study based on coral geochemical records in Indonesia shows that coral Sr/Ca and 18O from Indonesian records SST and salinity respectively. Coral Sr/Ca from inshore Seribu islands complex shows more air temperature rather than SST. Modern coral from Timor shows the impact of ENSO and IOD to the saliniy and SST is different at Timor sea. On interannual time scales, coral-based Timor SST and SSS are sensitive to the IOD, whereas ENSO only influences SST. ENSO influence strongly Timor SST and SSS on the decadal-scale variations. This result should be considered when interpreting Paleoclimate records over Indonesia. Our coral also shows more pronounced low frequency SST variability compare to the SST reanalysis (model). Sr/Ca recorded in fossil coral from medieval warm period i.e 0.85±0.02-0.81±0.03 kyBP shows that SST variability during medieval warm period larger than present SST recorded from modern coral. ENSO/IOD like signal is larger and more frequent than today.